PROBLEMS OF MODERN SCIENCE 



many still fainter, but a mathematical discussion 

 of the numbers actually counted leads to the 

 conclusion that the total number is finite. It 

 would appear that the stars of the twenty-fifth 

 magnitude are more numerous than those of any 

 lower or higher magnitude, and that the total 

 number of all magnitudes is of the order of 3000 

 millions. It may be remembered that Lord 

 Kelvin, reasoning from dynamical considerations, 

 estimated the number to be about 1000 millions. 

 These numbers are large, but so far as the mere 

 figures are concerned they may be compared with 

 our national debt of 8,000,000,000 or with the 

 population of the globe, which is estimated to be 

 about 2000 millions. 



We may next enquire what information can 

 be derived from these photographs regarding the 

 distribution of the stars in space. Distribution 

 depends upon distance and direction, and regarding 

 the former of these elements the photographs can 

 yield no direct information. It is obvious that the 

 dimmer stars must on the whole be more remote 

 than the brighter ones, but we now know that 

 estimates of distance based on apparent brightness 

 alone are likely to be much in error, because they 

 leave out of account the differences in absolute 

 brightness. As a matter of fact some of the faintest 

 stars are comparatively near us, while many of the 

 brightest are at a great distance. Disregarding, 

 5o 



